【LeetCode】Populating Next Right Pointers in Each Node

description:
Given a binary tree
    struct TreeLinkNode {
      TreeLinkNode *left;
      TreeLinkNode *right;
      TreeLinkNode *next;
    }

Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to  NULL .
Initially, all next pointers are set to  NULL .
Note:
You may only use constant extra space.
You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).
For example, Given the following perfect binary tree,
         1
       /  \
      2    3
     / \  / \
    4  5  6  7

After calling your function, the tree should look like:
         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \  / \
    4->5->6->7 -> NULL
code:
/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(root == NULL)
            return;
        queue<TreeLinkNode *> qu;
        qu.push(root);
        qu.push(NULL);
        while(true)
        {
            TreeLinkNode *cur = qu.front();
            qu.pop();
            
            if(qu.empty()) break;
            
            if(cur != NULL)
                cur->next = qu.front();
            else 
            {
                qu.push(NULL);
                continue;
            }
            if(cur->left)
                qu.push(cur->left);
            if(cur->right)
                qu.push(cur->right);
            
        }
    }
};

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